** Shares of drug developer Leap Therapeutics LPTX.O fall 67.1% to 74 cents premarket
** Co says it will not move forward with late-stage trials of its drug, sirexatamab, in patients with gastric cancer
** Says drug will show negative results for ongoing mid-stage trial's main goal of progression free survival when study completes
** Will explore partnership opportunities to test sirexatamab in combination with a type of cancer drugs called anti-PD-1 antibodies for treatment of gastric cancer and other diseases
** Up to last close, stock down 7.8% YTD
(Reporting by Christy Santhosh)
((Christy.Santhosh@thomsonreuters.com))